1. Field of the Invention
This invention relates to a solid waste comminution apparatus. Such devices have been established in the art and are now widely used in a variety of applications, such as municipal waste treatment and industrial applications. The devices typically employ two stacks of interleaving cutting elements to reduce solids. Structural elements to support the housings called side rails have been enhanced to not only provide support, but provide increased flow while still limiting the bypass of solids.
2. Description of the Related Art
Side rails are components of comminuting device designs, typically consisting of interleaved fins and slots, whose purpose is to intercept and redirect large particles in the waste stream into the cutter stack, while at the same time allowing water to pass through the slots between the fins. The leading surface of each fin begins at the inlet of the device and the trailing surface extends to the mid-depth of the comminutor or beyond. Water flow through the side rails is influenced by two factors, the gap distance and the length of flow passage between each fin. The leading surface of the fin is angled at the intended flow direction in an effort to direct material into the cutter stack (see Fig. III).
Referring to FIG. 1 of the drawings, a comminutor 10 is particularly useful in comminuting solid waste material borne by a liquid flowing through the interior of a casing 12. The casing forms a comminution chamber 14. The casing 12 is shown in vertical section to illustrate the components of the comminutor and the manner in which they achieve shredding of the solid waste. Purposely, this figure does not show the inlet port or outlet port which are on opposite sidewalls (not shown), into and out of the plane of the paper bearing FIG. 1.
The vertically upright, rectangular, cross sectional casing 12 includes a cast metal base 16 supported by a rectangular plate or cover 18 and bearing, in vertically upright position, a pair of side rails indicated generally at 20. Side rails 20 are connected at their bottoms by screws 22 to an upwardly projecting mounting plate 16a of base 16. At the top of casing 12, there is provided a mirror image cast metal casing head or upper frame member 24 of rectangular horizontal cross-section and which terminates, at it's bottom end, in a second mounting plate 24a. In similar fashion, further screws 22 project through the top of the side rails and are threaded within tapped holes (not shown) of head mounting plate 24a. 
The first and second shredding stacks at 26 and 28 are mounted in mutual, parallel alignment for counter-rotation on drive shaft 30 and idler or driven shaft 32, respectively. Shaft 30 is supported by an upper bearing assembly 34 within head 24 and by a lower bearing assembly 36 within base 16 respective. Shaft 32 is similarly supported for rotation about its axis and parallel to the axis of the drive shaft 30 by upper bearing assembly 38 and lower bearing assembly 40, respectively. In similar fashion to U.S. Pat. No. 4,046,324, the stacks 26, 28 may be compressed between opposing bearing plates (not shown) by nuts 41 on shafts 30, 32 backed by washers 43. The drive shaft 30 includes a drive gear 42 which is in mesh with a similar size driven gear 44 fixed to the upper end of the driven shaft 32. Rotation of the drive shaft 30 effects counter-rotation of shafts 30 and 32 about parallel axes. Drive is affected by an electrical motor indicated generally at 46 powered from an electrical source (not shown) through control box 48. A motor shaft (not shown) of the drive motor 46 is coupled mechanically to drive shaft 30 through a gear reduction unit indicated generally at 50 for driving the comminutor drive shaft 30 at an appropriate RPM suitable to the comminuting of particular solid waste material to which the unit has application.
As previously described, each of the stacks 26, 28 is formed of a number of laminar cutting elements which are preferably of disk form. The cutting elements are directly mounted on the shafts 30, 32. The shafts may be of hexagonal cross sectional configuration with the cutting elements having corresponding holes or openings through the center of the same. The cutting elements 52, 54 are positioned between and separated in the axial direction along respective shafts 30, 32 by laminar spacers 56, 58, respectively, in the form of circular disks of reduced diameter with respect to the cutting elements 52, 54. Preferably the thickness of the cutting elements 52, 54 and the spacers 56, 58 are the same so that the laminar spacers of one stack are coplanar with cutting elements of the other stack. Thus, a cutting element from one stack and a spacer from the other stack form together a pair of interacting shredding members. While cutting teeth (not shown) integral with the cutting elements and projecting radially thereof overlap each other to the extent of their root diameters, there is always a slight gap between the outer periphery of the cutting element teeth of one stack and the periphery of the opposed laminar spacer of the other stack. Insofar as the present invention is concerned, the make-up, assembly, and the nature of the drive imparted to the cutting elements herein can be identical to that of U.S. Pat. No. 4,046,324.
The related art also relied on fins along the side walls that were horizontal (U.S. Pat. No. 5,593,100) to direct large particles into the cutter stack while allowing liquid to pass through the comminutor. If the material is in thin strips or sheets, the side rail can be prone to “stapling” where a strip of material wraps around the leading surface of a fin in a U shape. Eventually, a build-up of stapled material will block the flow through the side rail requiring operator intervention.
Another patent (U.S. Pat. No. 5,160,095) utilizes slots at an angle from horizontal. This exposes material passing through the slot to multiple cutter disks in the effort to reduce possible bypass. However, this also results in a higher pressure drop across the device, reducing hydraulic capacity. This design also demonstrates a tendency for stapling as a result of the rake angle of the leading surface of the fin.
Related art fins are shown in FIGS. 2A-4B. Each side rail 20 has a number of fins 100 separated by slots 110. Each slot has a predetermined gap height 115 and length 120. The leading edge 130 is formed with a rake angle 125 measured with respect to an orthogonal to the side wall surface. The fins are placed with a clearance 140 to the cutter elements of no closer than 0.16″ in order to prevent unusually high pressure drops. The related art design is susceptible to stapling and inhibits flow in the wastewater system. The related art fins have a rake angle 125 of no less than 45 degrees.
Additionally, because of the large inlet to outlet pressure drop across the machine, prior side rail designs have large gaps between the side rail and the outside diameter of the cutter stack (typically on the order of 0.16″ or greater) to allow water to flow between. This can also allow material to bypass the cutter stack.
Side rails with enhanced flow properties, are components of comminuting device, typically consisting of fins and slots, whose purpose is to intercept and redirect particles in the waste stream into the cutter stack, while at the same time allowing water to pass through the slots between the fins. The ratio of the fin thickness to the opening creates the open area for the side rail.
Previous designs to increase flow capacity through the side rail were either achieved by spacing the side rail further away from the cutters to create a gap between the side rail and the comminutor cutting elements or removing all of the fins from the side rail, which created a similar large gap as well. While these designs increased the flow capacity of the comminuting device, sometimes by as much 35%, this method of design significantly decreased the devices ability to capture and reduce solids. The comminuting devices ability to reduce solids is its main purposed for being installed in a waste stream.